Jannik Sinner extended his lead in his budding rivalry with Carlos Alcaraz by defeating the top seed 7-6 (4), 6-1 in the China Open semifinals.

The two players had split their previous six matches, including a US Open quarterfinal that was arguably the best match of last year.

The first set of the Beijing match was a series of thrilling, hard-fought rallies, with 22-year-old Italian Sinner twice coming from a break down to win it in a tie-break.

And Alcaraz, 20, was unable to match his young rival in the second set, the errors beginning to flow in a win for Sinner, who struggled with sickness during his quarter-final on Monday.

"Every match against him is very tough," said the Italian. "We always show great respect. When we play against each other we try to stay on our limits and today I played a little bit better in the important moments.

"Today it was my day and let’s see in the next meeting what's coming. I always enjoy to play against him."

In the final, Sinner will take on second seed Daniil Medvedev, who again showed his hard-court prowess in a 6-4 6-3 win against Alexander Zverev.

Britain's Neal Skupski and Dutch partner Wesley Koolhof are through to the doubles final after a 7-6 (3) 6-2 win over Karen Khachanov and Andrey Rublev and will take on top seeds Ivan Dodig and Austin Krajicek.

Meanwhile, Australian Marc Polmans was defaulted from his qualifying match at the Shanghai Masters for hitting the umpire in the face with a ball.

Angry at not converting a match point against Italian Stefano Napolitano, Polmans smashed a ball hard towards the stands but struck British official Ben Anderson in a virtual replay of an incident involving Canadian Denis Shapovalov during a Davis Cup clash with Great Britain in 2017.

The umpire on that occasion, Arnaud Gabas, was left with a fractured eye socket. Thankfully, Anderson appears to have escaped serious injury, with a tournament representative saying he was struck on the cheek and nose and had returned to his hotel to rest.